When I edit my own comments, all is good. But when I as a moderator edit someone else's comment, the comment is deleted. (Using my powers to edit my own comment outside the five-minute window does not cause a problem.)
I only noticed this today, although Pat Ludwig said in chat that he thought it had happened to him a couple of days ago. Looks like the revision hasn't changed since the 24th, so that would make sense.
EDIT: Still a problem in rev 2011.1.2.1.